Abstract

Background

Like other vertebrates, primates recognize their relatives, primarily to minimize
inbreeding, but also to facilitate nepotism. Although associative, social learning
is typically credited for discrimination of familiar kin, discrimination of unfamiliar
kin remains unexplained. As sex-biased dispersal in long-lived species cannot consistently
prevent encounters between unfamiliar kin, inbreeding remains a threat and mechanisms
to avoid it beg explanation. Using a molecular approach that combined analyses of
biochemical and microsatellite markers in 17 female and 19 male ring-tailed lemurs
(Lemur catta), we describe odor-gene covariance to establish the feasibility of olfactory-mediated
kin recognition.

Results

Despite derivation from different genital glands, labial and scrotal secretions shared
about 170 of their respective 338 and 203 semiochemicals. In addition, these semiochemicals
encoded information about genetic relatedness within and between the sexes. Although
the sexes showed opposite seasonal patterns in signal complexity, the odor profiles
of related individuals (whether same-sex or mixed-sex dyads) converged most strongly
in the competitive breeding season. Thus, a strong, mutual olfactory signal of genetic
relatedness appeared specifically when such information would be crucial for preventing
inbreeding. That weaker signals of genetic relatedness might exist year round could
provide a mechanism to explain nepotism between unfamiliar kin.

Conclusion

We suggest that signal convergence between the sexes may reflect strong selective
pressures on kin recognition, whereas signal convergence within the sexes may arise
as its by-product or function independently to prevent competition between unfamiliar
relatives. The link between an individual's genome and its olfactory signals could
be mediated by biosynthetic pathways producing polymorphic semiochemicals or by carrier
proteins modifying the individual bouquet of olfactory cues. In conclusion, we unveil
a possible olfactory mechanism of kin recognition that has specific relevance to understanding
inbreeding avoidance and nepotistic behavior observed in free-ranging primates, and
broader relevance to understanding the mechanisms of vertebrate olfactory communication.